The invention concerns a magnetic filter that consists of a magnetic cylinder with stripper, pivot-mounted in a casing, sheathed in a casing at the bottom, whereby a flow channel for the medium to be filtered is formed between the cylinder and the casing.
The magnetic filter serves to remove magnetically conductive and non-conductive bits of dirt from coolants and lubricants so that they can be re-used. The degree of cleanliness of coolants and lubricants is a decisive factor in manufacturing precision and surface finish of processed machine parts. Improving the quality of the magnetic filter leads to an increase in the service life of tools, parts, and coolants and lubricants.
Automatic magnetic filters have long been known in modern technology, e.g., from U.S. Pat. No. 2,736,432 and from Swiss Pat. No. 459.107. The automatic devices most commonly in use are equipped with a long magnetic cylinder that consists of several magnetic fields. The magnetic cylinder, which is operated by a motor with reducing gear is housed in a casing which surrounds the cylinder from below. The medium to be purified is usually fed above the axle over the flow passage, which travels in the axial direction of the magnetic body, by the tractive power of the magnetic cylinder. The outlet on the opposite side is arranged in the same way, but is normally somewhat deeper, to guarantee a good flow. The magnetically attracted impurities contained in the fluid to be filtered collect on the magnetic cylinder in the form of beardlike clusters, with larger pieces of debris being attracted faster than small ones. The magnetic flux decreases as the distance between the magnets and the individual pieces increases. The smallest pieces that flow into the channel in the medium to be purified from the outside, that is, from the cylinder surface that is most distant, for the most part do not have sufficient time during the flow to reach the magnetic surfaces of the cylinder.
If in such a filter the rate or quantity of flow is reduced, the level at entry into the flow channel drops, the magnetic cylinder area acted upon becomes smaller, and the filter capacity thereby also becomes smaller. In the case of still smaller quantities, the medium to be purified washes over the inlet edge, thereby creating turbulences in the flow channel and thereby reducing still further the efficiency of the magentic filter.
The purpose of the invention is, on the one hand, to improve the efficiency of the magnetic filter, and on the other hand to maintain the flow conditions of the medium to be purified at their best, even in cases of reduced rate of flow.
According to the invention, this task is solved by making the profile section of the flow channel variable. Advantageously, at least a portion of the casing is mobile. However, provision can also be made for a slider that extends adjustably into the flow channel.
The medium to be purified is thus guided in the direction of the magnets after the first phase of stabilization and filtering out of the largest particles, on the one hand, and on the other hand, the magnetic flux during the approach of the particle to the magnet is strengthened. Decreasing the profile section of the channel produces an increase in the flow resistance, resulting in a backwash, so that even in cases of small quantities the level and hence the inflow characteristic of the filter approximately correspond to those of the full load quantity.
In a preferred form of embodiment, the magnetic filter has a control device which switches the driving motor of the magnetic cylinder on and off, depending on the fluid level.
Control of the rotation of the magnetic cylinder by means of a float is well known from Swiss Patent No. 459.107. However, a mobile control of this type is not sufficiently reliable, and it has too broad a control range to guarantee a continuous high efficiency rate.
These disadvantages are eliminated by the above-mentioned advantageous embodiment with an electrical control. Filter efficiency can best be automatically adapted to operating conditions and the physical qualities of the lubricants and coolants in conjunction with the variable profile section of the flow.